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Where I live, KOH is not readily available and is cost prohibitive to ship. A number of other materials are available, however. I have read similar questions and their answers here, but most are too general or too specific for me to understand.

I could mix NaOH and KCl, both of which are available, to yield NaCl and KOH. But I'm not sure how I would separate them, as I can't think of any readily available substance that could be used to precipitate out the Na.

Or, I could mix Ca(OH)2 and K2CO3, as that would produce CaCO3(s) and KOH(aq). However... I do not have K2CO3 available. I could make the K2CO3 myself, by baking NaHCO3 into Na2CO3 and mixing it with KCl to produce NaCl and K2CO3, but then I am back at having to precipitate out Na.

I could also make the K2CO3 by combining C and KNO3, but... again... I do not have KNO3 available. I could make KNO3 from KCl and NH4NO3, but that's not available here either.

I feel stuck. KCl, NaOH, and Ca(OH)2 are all available and relatively cheap. NaHCO3 and NaCl are also obviously available and cheap. What else am I missing here? What else is generally available and cheap that I could use to synthesize KOH?

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    $\begingroup$ It would be very difficult to separate Na+ from K+ once they are in aqueous solution, because salts of both are highly soluble. I don't see any easy way to do what you wish to do. Why do you need KOH specifically? Can't NaOH do the same job? $\endgroup$
    – S R Maiti
    Commented Jul 12, 2021 at 3:11
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    $\begingroup$ I am planning on making liquid soap, which requires KOH. NaOH makes solid soap. I just discovered that potassium bitartrate (cream of tartar) decomposes into potassium carbonate, though, so this may be promising. Currently researching this option. $\endgroup$
    – Jared Brandt
    Commented Jul 12, 2021 at 3:29
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    $\begingroup$ If you cannot get K2CO3 by easier way, you can get it by extraction of wooden ash, as this was the ancient way to get potash. $\endgroup$
    – Poutnik
    Commented Jul 12, 2021 at 5:32
  • $\begingroup$ @Poutnik I have read that wood ash leachate contains both potassium carbonate and potassium hydroxide. Is this a mistake? Or is there a way to limit it to only one or the other? Or to know the ratio in solution, so one could add an appropriate amount of calcium hydroxide to convert all the K2CO3 to KOH? $\endgroup$
    – Jared Brandt
    Commented Jul 12, 2021 at 5:57
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    $\begingroup$ "is cost prohibitive to ship" - Are you in an embargoed country or something? I find it hard to believe that KOH is cheaper to make than to ship just about anywhere in the world. It's one of the most heavily used industrial and commercial compounds in the world. Have you really exhaustively searched for a supplier and come up empty? You ask "What else is generally available and cheap that I could use to synthesize KOH?" - well, KOH is generally available and cheap, so you must be somewhere where generally available things are VERY hard to find. So where is that? $\endgroup$
    – J...
    Commented Jul 12, 2021 at 13:35

1 Answer 1

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If the only potassium salt you have is $\ce{KCl}$, then perhaps the only feasible way to get rid of the chlorine is electrolysis.

Using a cation-selective membrane, electrolysis in water will produce $\ce{KOH}$ (and hydrogen, $\ce{H2}$) at the anode, and chlorine, $\ce{Cl2}$, at the cathode (along with potassium hypochlorite, $\ce(KClO)$).

Though this will produce the $\ce{KOH}$, it also leaves you with hydrogen, chlorine, potassium hypochlorite and other byproducts which must be disposed safely. Further, the process is energy intensive. This could be done as a classroom demonstration, but commercially, you'd need to find good uses for the gases and bleach/disinfectant for any chance at economic feasibility.

If you can obtain potassium carbonate ($\ce{K2CO3}$) or "bicarbonate" (acid or hydrogen carbonate, $\ce{KHCO3}$), it can, with effort, be converted to $\ce{KOH}$ by heating. That said, decomposition temperature is ~1200 °C, which can be achieved in a ceramic kiln - barely. Again, this calls for a great deal of energy, so you'd pay far more for the cost of heating and the carbonate than for $\ce{KOH}$ alone. Also, at 1200 °C, the $\ce{KOH}$ evaporates, so it would have to be condensed on a cooler surface. It might also shorten the life of the kiln. On second thought, this sounds like a project that would be described in Derek Lowe's blog, Things I Won’t Work With.

@Poutnik suggests a displacement reaction with $\ce{Ca(OH)2}$, which would be far easier, but leaves the user to purify his product from remaining calcium -- calcium soaps tend to be insoluble.

In any case, $\ce{KOH}$ is very caustic: "CAUSES SERIOUS EYE DAMAGE. CAUSES SEVERE SKIN BURNS..." Use caution!

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  • $\begingroup$ What other potassium salts are generally available?? $\endgroup$
    – Jared Brandt
    Commented Jul 12, 2021 at 4:40
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    $\begingroup$ @Jaredbrandt K2CO3 is often available as well.// Just for curiosity - it is largely used in Dutch processing of cocoa ( cocoa gets from light brown to dark brown by the process ) to produce chocolate from inferior cocoa beans, enhancing cocoa flavour and removing acidity. $\endgroup$
    – Poutnik
    Commented Jul 12, 2021 at 7:33
  • $\begingroup$ Potassium bicarbonate is used in agriculture as a fungicide, and as a soil conditioner to control acidity. It is also used in dry powder fire extinguishers, and as an alternative to sodium bicarbonate (baking soda) in cooking by people on a low-sodium diet. Depending how pure you need it, you should be able to find a source for it somewhere. $\endgroup$
    – alephzero
    Commented Jul 12, 2021 at 12:58
  • $\begingroup$ I am curious, how would you easily convert K2CO3 to KOH by heating at home , assuming you cannot afford even KOH shipping. The medieval way M2CO3 + Ca(OH)2(from bricklayers) -> CaCO3 + 2 MOH seems to be much easier. $\endgroup$
    – Poutnik
    Commented Jul 13, 2021 at 10:15
  • $\begingroup$ @Poutnik, "a great deal of energy" was stated. Perhaps a pottery kiln? Decomposition temp ~1200 °C, which can be reached in a kiln. Amending answer for that.Admittedly, not easy to do. $\endgroup$
    – DrMoishe Pippik
    Commented Jul 13, 2021 at 21:49

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